Methane Hydrate Formation and Decomposition Properties during Gas Migration in Porous Medium

Natural gas hydrate is a clean energy source with significant potential. It's significant to elucidate the formation and dissociation properties of natural gas hydrate during exploitation process. In this study, methane hydrate reformation under dynamic conditions was simulated to provide essential data for hydrate safe and efficient exploitation. The changes of vessel pressure, methane hydrate saturation (Sh) and residual water saturation (RWS) were measured and analyzed. Residual water distribution is illustrated by images obtained by magnetic resonance imaging (MRI). The experimental results indicated that an optimum gas velocity exist to maximize hydrate generation under a certain initial water saturation when constant velocity of methane was injected into the porous media. Compared to downward methane, upward methane is more likely to cause structure changes of porous medium and the structure changes can't recover after hydrate dissociation. Comparing the axial residual water distribution porous media during the process of hydrate formation and decomposition, the axial residual water distribution in formation process is more non-uniform than that in dissociation process. Moreover, the hydrate dissociation boundaries moving from vessel wall to core can be observed by MRI images. This study provides important basic data for natural gas hydrate exploitation. (C) 2017 The Authors. Published by Elsevier Ltd.